GE polls are worthless all together for all candidates this far out and we should judge candidates on the issues that will affect their electability. Bernie is horrible in that regard.
I will say that if Bernie got Cruz or Trump in the general, he could win because those guys are unelectable also... but the margin would be far less than Hillary's margin, the potential of defeat much higher, and the Senate and House seats gained far fewer. If Bernie wins without a Senate with 60 Democrats and a House with 218 Democrats, then he's going to accomplish roughly zero of his major ideas and his presidency will basically be Hillary's except Hillary has a stronger grasp on executive actions.